Fibre Multi-Object Spectrograph (FMOS) is the next common-use instrument of Subaru Telescope. FMOS consists of three subsystems; the Prime focus unit for Infrared (PIR), the fibre positioning system/connector units, and the two infrared spectrographs. The PIR was transferred to the Subaru Observatory in the spring of 2005 to check the optical performance on the telescope. As a result of the test observation, we found that the adjustment of the optical axis between PIR and the primary mirror was difficult with the initial design of the corrector alignment stage. Furthermore, the optical axis of the telescope moved over a little owing to an earthquake in Hawaii Island in Oct. 2006. Therefore we decided to modify mechanical structure of PIR, the corrector alignment stage as well as the cable wrapping system. This modification was completed in the summer of 2007. In this proceeding, we report the mechanical structure of the new PIR and the results of the engineering observations.